1. Fixes bug where multiple ALCs were created if two extension dlls
     had the same parent directory.
  2. Provides better errors messages if extension paths are malformed.
  3. Normalizes which assembly contributes to the MEF composition if
     provided multiple times
  4. Loads analyzers provided by extensions into the same single extension ALC

  1. Ensure an assembly only contributes to the MEF catalog once
  2. Prefer the code base to load MEF assemblies
  3. Load devkit dlls via hooking AssemblyLoadContext.Default.Resolve
  4. Misc feedback

  1. Move duplicate checking to ExtensionAssemblyManager
  2. Store mapping of assembly full name to load context to allow MEF to
     load an assembly by name from the correct load context.
  3. Move devkit assembly resolution out of ExtensionAssemblyManager
  4. Misc feedback

…oading_vscode